Extensible boom mechanism for use with mobile cable salvage apparatus

ABSTRACT

An extensible mechanism, in which a first hydraulic cylinder and piston has a fixed reference for movement in an extension direction and also in a retraction direction. A second hydraulic cylinder and piston is moveable in both of these directions. Hydraulic fluid actuates the first and second hydraulic units in series, whereby actuation in the extension direction sequentially moves the first and second hydraulic piston and actuation in the retraction direction reverses the sequential order of movement of the two hydraulic pistons.

FIELD OF THE INVENTION

The present invention relates to an extensible mechanism for extendingand retracting one end of a device with respect to a fixed point locatednear the other end of the device. More particularly, the inventionrelates to an extensible mechanism such as a boom which can be extendedand retracted to position an element on one end of the boom at a preciselocation with respect to the apparatus on which the boom is mounted. Ina particular embodiment, the invention relates to a boom for positioninga sheave at a cable location, where the cable is underground oroverhead, so that a cable pulling device can pull the cable in astraight line from the conduit for a short distance prior to changingdirection of the cable and movement of the cable to the cable pullingapparatus.

BACKGROUND OF THE INVENTION

Public utilities use large amounts of underground electrical cable, suchas electric power cable, telephone and telegraph cable, railroad andother public transportation cable systems, fire and police departmentsand traffic control signal generation cables and the like.

The preferred place of installation of cables of these type are belowground in conduits which protect the cables from weather and which donot disrupt the environment, either from an aesthetic point of view orfrom the very real practical problem of supporting many cables onoverhead lines. Overhead lines have the further disadvantage of beingsusceptible to vandalism. In addition, they present potential danger tothe population when cables may fall because of accidents, storms and thelike.

However, even the best systems ultimately deteriorate. Underground cableeither deteriorates and must be removed or replacement may be requiredof the cable by one which is larger or which contains other features.Even when the cables are placed underground, there is a limit to thenumber of cables and conduits which can be installed and so, it isdesirable to remove old cable.

The process of cable removal can be expensive and difficult,particularly when many cables are packed together and separated by 400to 800 feet intervals, which is the typical distance between manholelocations, particularly in the city. One device which has been admirablyaccepted as apparatus for removing cable from underground conduits isshown in U.S. Pat. No. 3,736,822. In this patent, a cable puller isshown which is mounted on a truck and which removes cable from manholesand other underground locations, and thereafter cuts them intodisposable lengths. An improvement on that prior patent is disclosed inU.S. Pat. No. 3,799,016, in which an improved puller and an improvedcutter are disclosed.

While these devices have served admirably over the past years, industryhas been installing larger and more complex cables. As a result, thecables are more difficult to remove and, in some case in large cities,are at a depth which is 10, 20 or even up to 30 feet below the surfaceof the pavement. Nevertheless, it is important to remove cables oncethey have been phased out of service.

Not only is there a value in recycling copper, lead and other materials,in some municipalities cables are treated as real estate, resulting intaxation of the value of the installation. Vacant ducts significantlyreduce the tax assessment. Thus, even if a cable is no longer in use,until it is removed it remains a source of expense.

One difficulty which has arisen in removing cables from undergroundlocations, particularly as cables are larger and deeper, is that it hasbecome more and more desirable to pull cables in a direction alignedwith a true horizontal. If one can envision an 800 foot section ofheavily corroded cable packed in a conduit with other cables, one canreadily appreciate that tremendous force is necessary to pull the cableout of the conduit.

Efforts to extend the pulling boom into the manhole have not met withsuccess at all. In some instances, the cable access and the boom accessare misaligned, even by only as little as two or three degrees. Such adeviation induces a tangential stress moment which causes the cable torotate in the conduit. The cable, upon rotation in the conduit, eitherbecomes jammed in the conduit and cannot be removed or the cable issubjected to stresses which cause it to rupture or break. In eithercase, the ability to remove the cable has been frustrated.

Accordingly, it is an object of the present invention to provideapparatus for permitting cable to be withdrawn from conduits in ahorizontal direction, thereby optimizing the efficiency of the cableremoval apparatus.

Another object of the present invention is to provide a device for usewith prior art cable pulling designs while maintaining theself-contained mobility of these truck mounted assemblies.

Still yet another object of the present invention is to provide anextensible mechanism which allows hydraulic movement of a point in bothan extension direction and a retraction direction.

Other objects will appear hereinafter.

SUMMARY OF THE INVENTION

It has now been discovered that the above and other objects of thepresent invention may be accomplished in the following manner.Specifically, an extensible mechanism has been discovered in which aplurality of hydraulic means are provided. The hydraulic components movein both an extension direction and a retraction direction. The device ofthe present invention further includes means for actuating the varioushydraulic means in series, whereby actuation in the extension directionsequentially moves the hydraulic means in one order, and actuation ofthe device in the reverse or retraction direction reverses thesequential order of movement of the hydraulic means.

In another form, the invention relates to an apparatus for pulling cablein either a salvaging or installing mode. A mobile platform is providedwith a cable guiding assembling, including cable pulling wheel means.Cable cutting means may also be provided. A sheave is positionedproximate the location of the cable installation by an extensible meanswhich movably presents the sheave to provide a straight path between theinstallation and the sheave and a second straight path from the sheaveto the wheel. Axial rotation of the extensible boom allows precisealignment of the sheave at the conduit.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects of the present invention and the variousfeatures and details of the operation and construction thereof arehereinafter more fully set forth with reference to the accompanyingdrawings, where:

FIG. 1 is a side elevational view of a mobile cable scrapper, showingthe unit adjacent the manhole aperture, in which a downhole telescopingboom is shown in a retracted road travel mode. A dot and dash position,approximately horizontal, shows a first travel position of thetelescoping boom to lower the overhead height of the boom when in thedown-hole vertical position. The vertical dot and dash position is thenassumed prior to inserting the down-hole telescoping boom to the desiredworking depth.

FIG. 2 is a side elevational view similar to FIG. 1 but showing thetelescoping boom lowered to the desired working depth opposite to, andaxially aligned with, a cable conduit. The telescoping boom can then bemoved horizontally to abut against the inner rim of the manhole by meansof the floating hydraulically actuated supporting structure. The rearend of the truck is stabilized by the street jacks. The severed end ofthe cable is passed under a sheave that is mounted to the lower terminalend of the telescoping boom and then drawn up to a take up wheel of thecable pulling assembly. At certain depths, the lower end of the boom isbraced by an adjustable "stiff-leg" as shown.

FIG. 3 is an enlarged fragmentary sectional elevational view taken alongline 3, 3 of FIG. 2 showing the fixed angular displacement or offset ofthe telescoping boom housing with respect to the vertical center line ofthe cable pulling wheel.

FIG. 3a is an enlarged fragmentary sectional plan view illustrating thecastering of the sheave to align the pulled cable to the vertical planeof a cable pulling wheel. The cable pulling is superimposed on the fullline fragment of the telescoping boom and a sheave in dot and dashoutline.

FIG. 3b is a pictorial view of a stiff-leg used to support the lower endof the telescoping boom when pulling cable at greater depths.

FIGS. 4-7 are semi-schematic side elevational view showing thesequential extension of the telescoping boom with respect to a commonheight dimension, that extends from the road surface to the pivot pointof the boom housing.

FIG. 8 is an enlarged fragmentary sectional side elevational view of theupper terminal end and aperture of a manhole showing a insert placed inthe recessed pocket for the iron manhole cover. The telescoping boom ismade to bear upon this surface instead of the iron ring of the manhole.

FIG. 9 a schematic elevational view of the 2 stage master cylinder andthe associated telescoping boom, and related hydraulic circuit. In thisview the telescoping boom is in the fully retracted or travel mode.

FIG. 10 is a schematic elevational view similar to FIG. 9 but showingthe master cylinder and associated boom in the fully extended down-holemode.

FIG. 11 is a greatly enlarged elevational view of the telescoping boomor master cylinder removed from the supporting structure of the cablepulling apparatus, having portions broken away and in section and lengthof continuous detail removed between break lines in order to showdetails more clearly.

FIG. 12 is a still greater enlarged section elevational view of thetelescoping boom, and the two stage telescoping master cylinder showingdetails of construction. Again large lengths of continuous detail havebeen deleted between break lines in order to show details clearly.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in FIG. 1, a device generally shown by the reference numeral 10is attached to a truck 11. The device includes a cable removing boom 12which is supported by hydraulic pistons 13 and 14 near the back of thevehicle, and by hydraulic pistons 16 near the middle of vehicle 11.

The device for removing cable includes a cable pulling wheel 17 at oneend of the cable removal boom 12 and a cable cutting means 18 at theother end of boom 12. Vehicle 11 is stabilized by support jacks 19 in aconventional manner. A similar vehicle would be used for installingcable, since it would also be pulled through the conduit using a leadwire.

The present invention contemplates the extension of a telescoping boomassembly 20 having a sheave at its lower terminal end for transferringthe cable being pulled from a conduit from a horizontal direction to avertical direction leading up to the cable pulling wheel 17. Thus, whenpulling old cable for salvage or new cable for installation, the sameconcepts are employed.

The boom assembly 20 of the present invention includes a mountingbracket 21 for pivotally mounting boom assembly 20 on end 22 of boom 12.The boom 20 includes a housing 23 which pivotally mounts sheave 24 atthe outer end of the boom 20. When the boom 20 is to be operated, it isfirst partially extended as shown in FIG. 1, and then is rotated bymeans of hydraulic piston 25 to a vertical alignment or orientation. Thesheave 24 is lowered through manhole 26 to a point where the cable 27can be pulled in a horizontal straight line direction from conduit 28around sheave 24 and in a straight line up to cable pulling wheel 17.When the depth of the cable 27 is significant, such as perhaps as deep20 to 30 feet below the manhole 26, an auxiliary support such asstiff-leg 29 can be provided as shown in FIG. 3b so that the tendencyfor the sheave 24 to move from the vertical is resisted. Similarly, theone edge 26a of the manhole 26 can be used as a support tocounterbalance the force required to pull the cable 27 from the conduit28.

As shown in FIG. 3, the telescoping boom 20 is angled at angle alphawith respect to the axis of the pulling wheel 17, which is shown in thisfigure as being mounted on winch 31. Sheave 24 is still capable ofdrawing the cable from the conduit in a straight line and then cable 17travels between sheave 24 and pulling wheel 17 in a straight line. FIG.3a shows the castering effect of rotation of sheave 24 to align thecable 27 to the plane of pulling wheel 17.

In FIGS. 4, 5, 6 and 7, the various components of the telescoping boomassembly 20 of the present invention are shown. The mounting bracket 21functions as pivot point about the end 22 of conveyor and cutting boom12 as previously shown in FIGS. 1 and 2. The telescoping boom housing 23contains a main telescoping boom 33 which is fully retracted in FIG. 4,partially extended and labeled 33a in FIG. 5 and fully extended from theboom housing 23 and labeled 33b in both FIGS. 6 and 7. FIG. 7 alsoincludes a stinger boom 37 which doubles the extension of the boom toits maximum depth, thereby positioning the sheave 24 at its furthestdistance from the cable pulling wheel 17.

In its most compact form, shown in FIG. 4, the main boom 33 is fullyextended upwardly so that the sheave 24 is at its closest or mostretracted position to the boom housing 23 which in turn is fixedlymounted on the end 22 of cable boom 12. Through the use of hydraulics,as described herein below, the master cylinder 38 causes the firstpiston actuator assembly 39 to retract into the cylinder 38, therebycausing piston assembly 39 to be enclosed by cylinder 38 and extend boom33 to a length 33a. Piston assembly 39 further includes a nested pistonactuator assembly 41, which is in the extended position shown in FIGS. 4and 5. By further application of hydraulic fluid, as will be describedherein below, nested piston assembly 41 is also retracted into thealready combined master cylinder 38 and first piston assembly 39,thereby further extending the main telescoping boom 33 to its fullyextended position 33b. At this point, sheave 24 has been lowered to apoint below the manhole 26 and is aligned with a cable in a conduit, notshown in these views.

Also contained within the main telescoping boom 33 is a stinger boom 37which has sheave 24 attached thereto. Again, as will be described hereinbelow, hydraulic pressure causes the stinger boom 37 to extend, therebygiving a maximum depth into the interior of the chamber. The hydraulicsare arranged so that these hydraulic mechanisms function sequentially,whereby first piston assembly 39 is actuated, followed by second nestedpiston assembly 41, finally followed by the stinger boom 37 contained inmain boom 33.

When the cable 27 has been pulled and it is desired to remove thetelescopic boom 33 and sheave 24 from the manhole, the last extendedmember, stinger boom 37, is the first to be retracted, followed by theextension of second nested piston 41, followed by the extension of firstpiston member 39. Thus, the extension of sheave 24 is retracted in theopposite sequential order of hydraulic means.

Turning now to FIG. 9, the operation of the hydraulics of the preferredembodiment is described in detail, showing the device as would be seenin FIG. 4. Shown in FIG. 10 is the same device as would be seen in FIG.7.

Boom housing 23 mounts a hydraulic master cylinder 38 by means of abracket 43. The outer terminal end of piston assembly 41 is fixedlyattached to the outer terminal end of the boom assembly 20 by means of acapping bracket 42. Capping bracket 42 encapsulates and axially mounts ahydraulic motor, as later described. Bracket 42 itself is secured to theouter terminal end of the main boom 33.

The oil for the hydraulic system is contained in oil reservoir sump 46and is transferred via pump 47 through a three way valve 48. In FIG. 9,the valve 48 is shown in the off position, 48B, where no oil flowsthrough either oil flow path 49 or 51, but rather recycles throughrecycle line 50 back to sump 46.

As has been stated the arrangement in FIG. 9 shows the boom 20 in itsfully retracted position, such as in FIG. 4. Movement of valve spool 48to position 48C causes oil from pump 47 to flow along flow path 49 intooil port 52 and then into chamber 53. As the pressure builds up,hydraulic pressure against surface 54, having an area A1, will cause apiston 39 to move to the left in the figure. Surface 54, having area A1,is the surface on which the hydraulic pressure will operate.

Oil flow from chamber 53 also passes through oil port 55 into chamber56, again causing hydraulic pressure against surface 57, which has anarea A2. A2 is the second largest area which the hydraulic fluid willoperate on.

Oil then leaves chamber 56 along oil port 58, to oil path 59 and intooil port 61. Oil flows into port 61 and enters chamber 62, therebypresenting hydraulic pressure on surface 63. Surface 63 has an area A3.As oil pressure builds, it is opposed by oil on the other side of eachpiston. Until the oil can be displaced, however, the pistons cannotmove. First piston assembly means 39 recedes into master cylinder 38because oil can be displaced from cylinder 38. At this point, poppetvalve 78 opens. Once piston 39 has reached a stop, the pressure onsurface 57, having area A2, acts on piston 41 to cause it to move intothe interior portion of the piston assembly 39. Finally, when pistonassembly 41 has reached its end of travel, and opens poppet valve 73,oil can be displaced from chamber 76, which will cause piston 65 to movewithin cylinder 64, thereby moving stinger boom 37 which is attached tocylinder 64 by mounting bracket 66. Once the oil completely fillschamber 62 and causes the piston 65 to fully extend stinger 37, oilflows through oil port 67 and oil path 68 and back into port 69 andthrough into oil path 71. Until poppet valves 73 and 78 are open, oilcannot flow in the extension direction for any cylinder other than inthe sequential order desired.

Shown in FIGS. 9 and 10 is the flow from chamber 62 through port 67 line68 port 69 and line 71 into inlet 72. Oil then flows through inlet 72passed poppet valve 73, which is opened by compression of spring 74.Note that large chamber 76 has a significantly greater area than nestingchamber 77, so that the exposed portion of piston 41 for oil flow in thereverse direction will be only against surface 102, which has a surfacearea of A4. Similarly, compression of poppet valve 78 and spring 79allows the nesting portion of piston 39 to decrease in area from largechamber 81 to the nesting chamber 82. Thus, only surface 101, havingarea A5, will be exposed to hydraulic pressure in reverse direction.

Poppet 78 will be nested in small chamber 82 upon movement of the piston39 to the recessed position. Oil then flows through exit port 83 viabypass ports 84 and returns by line 51 to valve 48, using valve position48C, for return through line 50 into the sump 46.

In this schematic, oil from chamber 81 also passes to sump when slidevalve 86 aligns escape port 87 with oil flow path 88 to sump.

In another embodiment of the present invention, the stinger boom 37 andits associated sheave 24 may be angularly positioned with respect to theaxial center line of boom 20. To this end a hydraulic motor 91 isaxially positioned and fixedly mounted to the bracket 42 and has acentrally mounted shaft 64a which is an extension and integral part ofhydraulic cylinder 64. The shaft 64a within the hydraulic motor 91 mayhave affixed to it a vane, not shown, that is angularly displaceableabout the motor axis under the influence of hydraulic pressure fromeither line 93 or 94. The hydraulic cylinder 64 is equipped with twolongitudinal extending keys 97. Spaced 180° apart, the keys 97 engage intwo cooperating key slots 100a formed in the capping end bearing ring100 fixedly secured to the stinger boom 37. It can be seen then thatactuation of hydraulic motor 91 by pressurization of either line 93 or94 will cause either a clockwise or counter clockwise rotation of shaft64a and integrally connected cylinder 64 and then through the interengagement of key 97 and keyways 100a in end bearing ring 100 acorresponding rotation will be transmitted to the stinger boom 37 andits attached sheave 24. Three way valve 92 allows flow path 92A and 92Cfor transferring oil along flow lines 93 and 94 to turn eithercounterclockwise or clockwise in the direction shown in FIG. 10 by arrow95. The lines 93 and 94 are flexible lines whereby movement of thetelescoping boom 20 is neatly controlled by means of a spring biasedreel 90.

It is necessary to align the sheave to the cable. In this manner, theterminal end of the cable conduit 28, sheave 24, the vertical rise ofcable 27, and cable pulling wheel 17 all will lie within a common planewhen sheave 24 is adjusted using motor 91.

In still another embodiment of the invention as shown in FIGS. 9 and 10,a safety feature has been included to prevent the ejection of stingerboom 37 from the main boom 33 in the event a failure should occur at theweldment 64b. Weldment 64b shown in FIG. 12, forms the actual physicalconnection of hydraulic cylinder 64 to hydraulic motor shaft 64a. Toprovide a safety device, the capping end bearing 100 has acircumferentially extending tapered grove 120. The groove is deepesttoward the sheave mounted end of the boom 37 and shallowest at the innerterminal end of the bearing 100 toward the hydraulic motor 91. Thetapered groove contains a circumferentially extending array of spacednylon balls 122. The balls 122 are of a diameter the same as the deepestportion of the groove 120. As the stinger boom 37 is extended by meansof a piston actuator 65 the balls 122 move up the slope of the taperedgroove 120 and exert an increasing braking pressure or drag on the innerdiameter of the main boom 33. When the stinger boom 37 is retracted, theballs 122 ride down the slope of the tapered groove 120 releasing thewedging or drag effect.

When the device is in the position shown in FIG. 10, in schematic,operation of the oil in the direction shown by the arrows along lines 49and 51 will have caused movement of pistons 39 and 41 to the positionsshown in FIG. 10. Reversal of the oil flow, such as by adjusting valve48 to position 48A, will cause oil to flow first through line 51 andreturning through line 49. When this happens, oil flows through poppetvalve 78, then through poppet valve 73, then along axial port 72 andultimately into chamber 62 to present oil pressure against surface 63A,which has surface area A3.

As pressure builds up, area A3 on surface 63A is the largest area whichsees hydraulic pressure and therefore piston 65 is the first to move,retracting stinger boom 37 from the position shown in FIG. 7 to theposition shown in FIG. 6. While oil pressure still continues to build upand piston 65 has travelled to its end position, shown in FIG. 9, oilbears on surfaces 101 and 102. Since surface 102 has an area A4 which isgreater than the surface 101 area A5, the hydraulic pressure will firstcause piston 41 to expand and move the piston 41 out of the nestingchamber 77.

Once this occurs, of course, the area seen by piston 41 is much greaterand piston 41 moves to the position shown in FIG. 9 again. Finally,pressure on surface 101, which has area A5, causes this smallest of allof the surfaces to move so that the valve comes out of nesting chamber82. Again, then, the piston 39 moves to its extended position, therebyretracting the last portion 33a of the telescoping boom 33. In eachcase, the movement of the various pistons and booms is governed by therelative ratio of the surface area in the chamber where oil pressure isseen.

The master cylinder 38 has a fixed reference for movement in both anextension direction and a retraction direction, since it is fixedlymounted to the telescoping boom housing 23. Area A1 is presented byfirst nesting piston 39 for movement in the extension direction and areaA5 for movement in the retraction direction. Auxiliary cylinder 64,which is also mounted fixedly to the housing 23, includes a piston 65which has an area A3, shown as 63 and 63A, which is the same area A3 formovement in both the extension direction and the retraction direction.

Finally, the second nested piston 41 has a surface 57 which has area A2for movement in the extension in direction and surface 102 having areaA4 for movement in the retraction direction. The hydraulic lines providefluid to the master cylinder 38 and the auxiliary cylinder 64 in series.

Since poppet valves 78 and 73 prevent oil displacement out of sequentialorder, fluid pressure in the extension direction sequentially movespiston 39, and thereafter piston 41, and thereafter piston 65. Sincearea A3 is greater than area A4, which in turn is greater than area A5,fluid pressure in the retraction direction reverses the sequential orderof movement of said pistons, so that piston 65 moves before piston 41and piston 41 moves before piston 39. Thus, the sequential order ofmovement of the extension boom in the extension direction moves inseries as oil is displaced in cylinder in series. Retraction draws inthe least substantial first and then eventually to the most substantialportion of the boom assembly.

Turning now to FIG. 11, there is shown a greatly enlarged elevationalview of the telescoping boom and master assembly after it has beenremoved from the supporting structure of a cable pulling apparatus.Break lines are shown to allow the entire length of the device to beplaced in one figure. The master cylinder 38 once again accommodates thefirst nested piston assembly 39 and a second nested piston assembly 41as described previously. The pivotal mounting bracket 21 provides afixed point of movement with respect to the bed of the vehicle or anyother fixture to which the device is attached. Boom housing 23 is ofcourse mounted firmly to the mounting bracket 21. Both pistons 39 and 41are fully extended, thereby placing the apparatus in its retractedposition, so that sheave 24 is closest to the point of reference,symbolized by mounting bracket 21. As has been previously described,when nested piston assemblies 39 and 41 retract, by hydraulic fluidpassing in series through the various hydraulic cylinders, the main boomis extended. Thereafter, the stinger boom 37 is extended so that theoperation is sequential. In withdrawing or retracting the sheave 24 to aposition closest to the mounting bracket 21, stinger boom 37 retractsfirst, then followed in sequence by movement of second nested pistonassembly 41 and finally movement of first nested piston assembly 39.This is a sequential operation in the reverse order from the extensionoperation.

Shown in FIG. 12 is an even greater enlarged sectional elevational viewof the present invention and the multiple stage telescoping cylinders,showing further details of construction, such as the existence of sealsand the like. This view and FIG. 11 show the actual design as comparedto the schematic drawings of FIGS. 9 and 10. The reference numbersapplies to all the figures are applied again in FIGS. 11 and 12 to thesame parts.

Of particular interest in FIG. 12 is the showing that the oil flow pathfrom one cylinder to another in series, thereby sequentially extendingthe moveable end and retracting that end in a reverse sequential order.

While particular embodiments of the present invention have beenillustrated and described herein, it is not intended to limit theinvention, and changes and modifications may be made therein with thescope of the following claims.

What is claimed is:
 1. An extensible mechanism, comprising:mastercylinder means having a fixed reference for movement in an extensiondirection and a retraction direction; first piston means in said mastercylinder, having means for displacing oil in said master cylinder formovement in said extension direction and a first piston area formovement in said retraction direction; an auxiliary cylinder on saidfixed reference, including an auxiliary piston means having means fordisplacing oil in said auxiliary cylinder and an auxiliary piston areafor movement in said retraction directions; and hydraulic means forproviding fluid to said master cylinder and said auxiliary cylinder inseries, to permit sequential displacement first in said master cylinderand then in said auxiliary cylinder and wherein said auxiliary pistonarea is greater than said first piston area, whereby fluid pressure inthe extension direction sequentially moves said first piston andthereafter said auxiliary piston and fluid pressure in the retractiondirection reverses the sequential order of movement of said pistons. 2.An extensible mechanism, comprising:master cylinder means having a fixedreference for movement in an extension direction and a retractiondirection; first nested piston means in said master cylinder, havingfirst oil means for displacing oil in said master cylinder for movementin said extension direction and a first piston area for movement in saidretraction direction; an auxiliary cylinder on said fixed reference,including an auxiliary piston means having means for displacing oil insaid auxiliary cylinder and an auxiliary piston area for movement insaid retraction directions; second nested piston means in said firstpiston means, having second oil means for displacing oil in said firstpiston means for movement in said extension direction and a secondpiston area for movement in said retraction direction; and hydraulicmeans for providing fluid to said master cylinder and said auxiliarycylinder in series, to permit sequential displacement in said first oilmeans, said second oil means and then said auxiliary cylinder, andwherein said auxiliary piston area is greater than said second pistonarea, which is greater than said first piston area, whereby fluidpressure in the extension direction sequentially moves said first pistonand thereafter said second piston and thereafter said auxiliary piston,and fluid pressure in the retraction direction reverses the sequentialorder of movement of said pistons.
 3. The mechanism of claim 2 whichfurther includes axial adjustment means for rotating at least one ofsaid piston means about the axis of said extension direction.
 4. Amechanism for actuating an element between extended and retractedpositions, comprising:master cylinder means having a fixed reference formovement in an extension direction and a retraction direction; firstnested piston means in said master cylinder, having first oil means fordisplacing oil in said master cylinder for movement in said extensiondirection and a first piston area for movement in said retractiondirection; an auxiliary cylinder on said fixed reference, including anauxiliary piston means having means for displacing oil in said auxiliarycylinder and an auxiliary piston area for movement in said retractiondirections; second nested piston means in said first piston means,having second oil means for displacing oil in said first piston meansfor movement in said extension direction and a second piston area formovement in said retraction direction; and hydraulic means for providingfluid to said master cylinder and said auxiliary cylinder in series, topermit sequential displacement in said first oil means, said second oilmeans and then said auxiliary cylinder, and wherein said auxiliarypiston area is greater than said second piston area, which is greaterthan said first piston area, whereby fluid pressure in the extensiondirection sequentially moves said first piston and thereafter saidsecond piston and thereafter said auxiliary piston, and fluid pressurein the retraction direction reverses the sequential order of movement ofsaid pistons; said master cylinder and auxiliary cylinder beingpositioned with respect to said fixed reference such that movement ofsad first piston means and said second position means in one directionwith respect to said fixed reference and movement of said auxiliarypiston means in the opposite direction with respect to said fixedreference produces additive movement of said element to said extendedand retracted positions.